Hi All,
Well, it finally happened - locked the wheel when I'd balanced the sails to self steer (ie without the Raymarine ST4000 MK2 Autopilot) and sailed along peacefully for a few hours with only the swish of the water instead of the usual aaaark, aaark of the Autopilot stepper motor - so nice.

Time to head for home - set a way point, engage the Autopilot clutch, GOTO Waypoint. Horrible graunching noise from Autopilot stepper motor. ****, forgot to unlock the wheel...too late, damage is done.

Pull the Autopilot motor/gearbox assembly apart and 3 of the 9 plastic gears in the plastic planetary gearbox are stripped. Gears are simple spur gears 24 teeth, OD approx 14mm, hole dia 4mm - similar hobby ones cost around $5 ea. Problem is are they Metric, Imperial, British, etc?
New Ramarine A18088 gearbox (their part no, but obviously none of it made by them) about $400 from UK.

Stepper motor is a Mabuchi RS-555-SH in a waterproof housing made by Raymarine.

So, would anybody know, have a clue maybe, on the manufacturer/model of the gearbox?

long shot I know, but worth a try..

btw, in the process, have turned up parts list, diagrams, etc of the ST4000 MK2 - pm me for a copy.